Secondary emission trigger circuit



March 10, 1953 R. K: STEINBERG 2,631,233

SECONDARY EMISSION TRIGGER CIRCUIT Filed Dec. 28, 1950 I50 vdl'rs 25E OUTPUT (5/ -|OO volts Q 3nnentor RICHARD K. STE INBERG Patented Mar. 10, 1953 SECONDARY EMISSION TRIGGER CIRCUIT Richard K. Steinberg, Poughkeepsie, N. 11., assignor to International Business Machines Corporation, New York, N. Y., a corporation of New York Application December 28, 1950, Serial No. 203,193

4 Claims.

This invention relates to electronic switches and more particularly to an electronic trigger circuit of the secondary emission type using a single electron tube and having two stable conditions alternately assumed.

One conventional type trigger circuit of the secondary emission type, when in one stable condition, has the secondary emittin surface at a potential with respect to the cathode such that it is insuiiicient to create a secondary emission ratio greater than one. As a result, when the trigger begins to switch to its other stable condition, the secondary emission ratio must first attain a value greater than one, and then the trigger must arrive at its other stable condition after the emitting surface either becomes more positive than the electron collector or some other predetermined condition of electrical stability is reached. One of the disadvantages of such a trigger resides in the fact that the time required for the switching of the trigger is increased because of the requirement that a secondary emission ratio greater than one must first be attained during the switching time, thereby increasing that time.

A principal object of this invention is to provide a trigger circuit of the secondary emission type which eliminates the above disadvantage and switches from one stable condition to the other in less time than conventional trigger circuits of the secondary emission type.

Another object is to provide an improved electronic trigger circuit of the secondary emission type having two stable conditions and utilizing only one electron tube.

A further object is to provide an electronic trigger circuit of the secondary emission type wherein the potential difference between the secondary emitting surface and the cathode is sufficiently large when the circuit is in either stable condition to create a secondary emission ratio greater than one.

A still further object is to provide a trigger circuit of the secondary emission type which is switchable to either of its two stable conditions by the application of only a single preselected electrical change to a predetermined place in the circuit.

Another object is to provide a trigger circuit of the secondary emission type wherein maximum flow of secondary electrons from the dynode is initiated immediately upon the application of an electrical change to the circuit to efiect a switching thereof. I Other objects'ofthe' invention will be pointed out in the following description and claims and illustrated in the accompanying drawing, which discloses, by way of example, the principle of the invention and the best mode, which has been contemplated, of applying that principle.

The drawing is a circuit diagram showing an embodiment of the invention.

In the following description a dynode is intended to mean an electrode which has a secondary emitting surface with a secondary emission ratio greater than one for a portion of the energy rang of electrons which may strike the surface.

Briefly, the invention comprises a novel trigger circuit of the secondary emission type having two stable conditions and utilizing only a single electron tube. In one stable condition the tube is non-dynode current conductive; this condition is termed the off condition. In the other stable condition the tube is dynode current conductive; this condition is termed the on condition. When in the off condition, the relative voltage between the dynode and cathode of the tube is suflicient to create a secondary emission ratio greater than one. However, the circuit arrangement is such that conduction of the tube is prevented. The subsequent application of a pulse to a single place in the circuit causes the tube to be rendered dynode current conductive and to quickly assume the on condition, since the secondary emission ratio is greater than one when the pulse is applied.

The description of the novel trigger circuit of the invention is undertaken with reference to the values of the applied voltages and the values of the circuit components used. These values are given to afford an easy understanding of the values of the voltages applied at various points within the novel trigger circuit of the invention, and it is understood that such values are for the purpose of example only and may vary over a wide range without altering the invention.

Referring more particularly to the drawing, the trigger circuit comprises an electron tube i0 operably connected between the voltage supply terminals H and l21to which is applied and l00 volts, respectively. A voltage divider comprising the resistors I3, 14 and I5 of 300,000, 270,000 and 200,00 ohms, respectively, is connected between the voltage supply terminals ii and i2. A second voltage divider comprising resistors i5 and I! of 51,000 and 24,000 ohms, respectively, is also connected between the terminals l I and [2. The cathodeof the tube I 0 is connected to a point Zllintermediate thev resistors 16 and H. The control grid of the tube 10 is conhosted through a limiting resistor 2| to a point 22 intermediate the resistors l4 and I5, and the collector grid is connected directly to the +150 volt terminal H. The dynode of the tube i is connected to a point 23 intermediate the resistors l3 and I4 and should have a surface which provides high secondary emission, for example, such a dynode may consist of an alloy of silver and magnesium properly processed in any conventional manner to give the desired surface.

From the values given, it is seen that the oathode, control grid and dynode are initially at 20 volts, -35 volts and +52 volts, respectively. The voltage difference between the cathode and dynode is therefore 72 volts, which is sumcient to ensure a secondary emission ratio greater than one. If the tube were conductive, there would be a net fiow of electrons away from the dynode. However, the negative control grid bias of volts is sufficient to maintain the tube non-conductive and the trigger circuit remains in the oii condition.

if a positive voltage pulse of suiiicient amplitud is applied to the terminal 2 to which the coupling capacitor is connected, it will cause the tube to conduct. Electrons pass from the cathode through the collector grid and strike the dynode. The secondary emission ratio is immediately greater than one, and there is a net flow of electrons from the dynode to the collector grid. The fact that the secondary emission ratio is immediately greater than one provides a faster switching trigger than would be provided if this ratio was attained subsequent to the conduction of the tube. This flow of electrons causes the voltage at the dynode to increase until it is approximately equal to the voltage at the collector grid, which voltage is approximately +150 volts. The exact voltage to whichv the voltage on the dynode will. rise will be determined by the loading caused by the voltage divider comprising the resistors l3, l4 and I5. This loading is minimized by choosing resistors of large ohmic value. The control grid finally reaches a potential. of approximately +7 volts as, does the cathode. The cathode. current passes through the resistor I? and, if the cathode voltage rises above approximately +7 volts, the negative bias thus created with. reference to the control grid voltage causes a decrease in the cathode current and a corresponding, decrease in the. cathode voltage,

The trigger is now in the on condition; any reduction in current through the tube causes a less negative grid bias which tends to increase the current, and any increase in current causes a more negative grid bias which tends to decrease the current.

The trigger may be returned to the off condition by applying a negative pulse of suitable amplitude to the terminal 2-5 thereby driving the control grid bias to cutoff.

A terminal 25 is connected through a capacitor 2? to the cathode of the tube it. It is seen that the trigger circuit may be switched from the off to. the on. condition by a-negative pulseapplied to the terminal 26 and from the on to the off" condition by a positive pulse applied thereto; Obviously, these pulses are of opposite polarity to those used when the trigger is switched in response to pulses applied to the terminal 24. Switching can be effected with equal facility by the application of the proper pulse exclusively to either terminal 24 or 26 or by pulses to either terminal in any desired sequence.

Terminal 28 connected directly to'the point 20 intermediate resistors 16 and H provides a neg-- ative voltage when the trigger is in the ofi" colidition and a positive voltage when the trigger is in the on condition. Obviously, output may be taken at any point along the resistors l3, I4, I5, IE or H.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to a preferred embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

A secondary emission type trigger circuit having two stable conditions including two voltage supply lines; two voltage dividers each connected between said lines; and an electron tube having a cathode, a control grid, a collector grid, and a dynode, each connected to one of said voltage dividers, so that said control' grid is normally biased below cutoff and the voltage difierence between said cathode and said dynode is sufiicient to create a secondary emission ratio greater than one; a pulse source for producing alternately positive and negative voltage pulses; and means coupling said source to said control grid to switch said trigger circuit from one stable condition to the other and means coupling said pulse source to said cathode to switch said trigger circuit from said other stable condition to saidone stable condition.

2. In a trigger circuit of the secondary emission type employing a single electron tube and having on and off stable conditions corresponding to the dynodecurrent conduction and non-conduction respectively of said tube; circuit and voltage means connected to bias said tube sufliciently to create a secondary emission ratio greater than one when itis' in the off condition; a source for producing successive pulses of opposite polarity; circuit means coupling said source to preselected points insaid trigger circuit for applying said pulses to said trigger circuit to switch it from one'sta'ble condition to theother.

A- secondary emission type trigger circuit having two stable conditions, including two volt age supply lines; two voltage dividers, eachconnected to one of said lines; anele'ctron tube having a cathode, a control grid; a collector grid, and a dynode, each connected toone of said voltage dividers, sothat said control grid is normally biased below cutoff and the voltage differencebetween said cathode and said dyno'de is sufficient to create a secondary emission ratio greater than one; a first pulse source and a connection therefrom to the control grid of said tube, so that the application of a pulse to the control grid causes said trigger circuit to be switched from one stable condition tothe other" stable condition; a second pulse source and a connection therefrom to the cathode of said tube, so that the application of a pulse to the cathode causes said. trigger circuit to be switched from said other stable conditionto said one stable condition.

' 4. A secondary emission type trigger circuit having two stable conditions, includingtwovoltage supply lines; two voltage dividers, each. connected to one of' said lines; an electron tube having'a cathode, a control grid; a collector grid}: and a dynode, each connected to one of-saidvoltage dividers, so that said'control grid is normally biased below cutoff and the voltage difference between said cathode and said dynode is sufficient REFERENCES CITED to create a secondary emission ratio greater than The following references are of record in h one; a source for producing a series of pulses me this Patent; 7 each having a polarity opposite to that of the pulses occurring just prior to and subsequent to 5 UNITED STATES PATENTS it in time; connections from said source to points Nul'nber Name Date in said trigger circuit, so that said trigger circuit 2 270 405 Black Jam 20 1942 is switchable from each stable condition to the .r other in response to said pulses.

RICHARD K. STEINBERG. l0 

